Conventional measurement methods for determining RF shielding effectiveness of a shielding structure typically use antennas, loops, radiating pins, transfer impedance, external signals, and various plate structures to determine the shielding effectiveness. Each of these have one or more of the following problems especially when determining the shielding effectiveness of a structure such as an RF shielding enclosure module with an RF gasket: (i) lack of the desired characteristic of module mechanics and gasket together, (ii) excessive size for module level, (iii) limited frequency range, (iv) limited dynamic range, (v) the probe can't be measured without mechanics, (vi) reliability of contacts that are part of the test set-up, but not a part of the measured system, (vii) isolation can be measured only to external world and not between two compartments.
A prior art document which deals with determination of shielding effectiveness is the patent U.S. Pat. No. 4,789,829, which describes a method which is based on current sensing between two electrodes. However, this method is not applicable to measuring the shielding effectiveness of a shielding enclosure module and an RF gasket together.
Another prior art document which deals with determination of shielding effectiveness is the patent DE19920986, which describes a shielding quality assessment method based on comparison of LF or MF broadcast signal field strength within and outside a screened area. This method has the drawback that it only characterizes isolation to the external world, and is suitable only for large spaces such as rooms and buildings.
An article which describes the state of the art in teseting of electromagnetic shielding is “Microwave Testing of Electromagnetic Shielding on Printed Wiring Boards”, by M. Vahtola and T. Tarvainen, in International Conference on Advanced Applications in Electromagnetics—ICEAA01, 2001, pp. 339–342. This article describes a method using isolation measurement between two short circuited pins.
A further illustrative article is “Effect of apertures in multiple EMI enclosures on RF printed circuit boards” by Clupper T., in IEEE EMC International Symposium, Aug. 13–17, 2001, Montreal, Canada, pp. 276–277. This article describes a method using isolation measurement between two loops. This method has the disadvantage that the dynamic range of the measurement is limited.